This invenion relates to an apparatus for and method of pneumatically unloading dry particulates from storage hoppers.
The unloading of dry particulates, especially those such as precipitated calcium carbonate and titanium dioxide which exhibit poor flow characteristics, from such as bulk hopper railcars and trucks presents a constant problem to handlers of bulk solids. The particulate material is commonly discharged from such a hopper through one or more bottom outlets in the hopper and pneumatically conveyed through a discharge line either directly to a process area utilizing the material or to a temporary storage bin. As the material flows through the hopper outlet, an air cone or "rat-hole" tends to develop above the outlet and flow of the material eventually stops.
This effect is commonly overcome by the use of portable vibrators attached to the car or truck through special brackets mounted on or near the hopper outlet. With current practice, the vibrators are usually operated continuously throughout the unloading period, high impact vibration being required to promote flow of those materials with poor flow characteristics. This continuous, high impact vibration causes structural failure to the hopper and compounds the flow problem by further densifying the material.
Since hopper cars and trucks are normally constructed of lightweight materials with minimum structural support in order to maximize payload, it is not practical to increase the strength of the structure to withstand the increased vibration. Instead, a trapezoidal shaped plate is usually welded to the hopper near the outlet and the vibrator bracket then welded to this plate. Mechanical failure generally occurs where the plate is welded to the thinner metal of the hopper.
This problem is particularly troublesome in manufacturing plants such as paper mills where many bulk commodities are received and an operator may be engaged in the unloading of several materials at the same time. Unless he is very attentive, the operator may not notice when a hopper is empty, and the resulting high impact vibration of the empty hopper is especially damaging.
It is therefore the primary objective of the present invention to provide an apparatus and method for pneumatically unloading such particulate material from storage hoppers which assures a substantially continuous flow of the material from the hopper with a minimum of mechanical damage to the hopper.